Prior art types of hand-held tire gauges include both the well-known mechanical tire gauge and the more recent digital tire gauge. The hand-held mechanical tire gauge includes a housing and a stem normally held inside the housing and having numbers on the stem which indicate the amount of tire pressure. When the mechanical tire gauge is placed on the valve stem of a tire to measure pressure, the pressure forces the numbered stem from the housing. The pressure is read from the stem by reading the number which is closest to a point where the stem exits the housing. While the mechanical tire gauge is inexpensive, the mechanical tire gauge suffers from being somewhat inaccurate because of its construction and the fact that the operator must judge where the stem meets the housing to determine pressure.
More recently, digital electronics have been incorporated in a hand-held device to measure the tire pressure electronically. The digital tire gauge typically includes a pressure transducer, an analog to digital (A/D) converter, a microprocessor, a light emitting diode (LED) or a liquid crystal display (LCD) for displaying the measured tire pressure, and a battery for powering the electronic circuitry. These types of digital tire pressure gauges tend to be more accurate than the mechanical tire pressure gauge but such gauges are also much more expensive due to the cost of digital electronics in general and the cost of A/D converters, in particular.
In these gauges, the A/D converter is used to digitize an analog pressure signal generated by the pressure transducer. This digitized pressure signal is then sent to the microprocessor which converts the digitized pressure signal into one which can be displayed on the digital display. Typically, a reading is made by connecting the digital tire gauge to the valve stem and pushing a button on the gauge to begin the pressure reading. The tire pressure reading is displayed on the digital display for a certain period of time sufficiently long to enable the operator to read the tire pressure value. Once this time period has elapsed, the digital tire gauge turns itself off to save battery power.
While current digital tire gauges do make accurate readings because operator judgement is removed from the measuring process, these tire gauges can be extremely expensive relative to the price of the mechanical tire gauge. In addition, such digital tire gauges power up all internal circuitry at the press of the button even if the gauge is not completely engaged to the valve stem. Consequently, valuable battery power can be wasted. Some digital tire gauges, therefore, use lithium batteries which while increasing the number of pressure readings between battery replacement also substantially increase the device cost due to the relative high cost of lithium batteries. Consequently, what is needed is an inexpensive electronic tire gauge which is highly accurate and increases the length of time between battery replacement or eliminates the need for a battery altogether.